I feel the language (the stream's "xml:lang" attribute) should be in the Session interface rather than the Connection (similar as the stream id), because it's unrelated to the session's transport.

The HttpSession already did that.

Otherwise the used language is not easy to retrieve, e.g. when using SessionManager to get the session and OF-208 is hard to solve.

Alternatively we can expose the Connection in the Session interface, but this approach feels wrong to me.

Also use `java.util.Locale` rather than String, because it better reflects what can be in `xml:lang` (it can also have country codes, e.g. "de-CH")

Archive legacy sources for Jive tools

These sources were added to support the pending Maven refactor (PR
#361). However the classes are not needed for the core compile/build.
Moved into separate archive for safekeeping.

The new Version.java comparison in master branch evaluates '3.11.0' as newer than '3.11.0 alpha' (which is correct), but causes a problem when attempting to load plugins requiring '3.11.0' on a developmental '3.11.0 alpha' release.

Modernize PluginManager internals with Java NIO.2 File API.

Generify ClusterTask interface

Support mock testing

OF-974: Migrate cache content

Add Legacy Jive build code for eventual removal

When switch to/from clustered deployment, ensure that critical cached
items such as components and remote servers are not inadvertently
dropped from the cache.

By replacing Jetty 6.x era libraries with 9.x-based variants, JSP support
will be brought back up-to-date. Additionally, Openfire will no longer
have a mix of dependencies from various versions of Jetty. This commit
contains a number of changes that go hand-in-hand:
- Replaces JAR files
- Applies uniformity to the buildscript where JSPC is executed
- Replaces JSTL 1.0 taglibs with later versions
- Adds a simple logger to the build process (to stop it from complaining)

in the same fashion as e.g. `java.util.concurrent.Callable`

Provide public constructor

Remove "private" default constructor to enable subclasses, mock
testing,, etc.

Various improvements in Version class

byte[].equals() should probably be Arrays.equals()

Adding PropertyListener support to AuditManagerImpl

StringUtils: Simplify verbose/duplicate and obsolete code constructs

Replace deprecated JiveConstants.XMPP_DELAY_DATETIME_FORMAT usage

OF-868 update roster cache on userModified

Tests should retrieve resources from the classpath rather than files.

Delete ChannelInputStream.java.

Cleanup connection logging, etc.

Update protocol support documentation.

Modernize XMLProperties with Java NIO.2 File API

Delete URLUTF8Encoder.java in favor of java.net.URLEncoder.

Revert PR#300 (restore PluginClassLoader)

per discussion with core team

Also remove dependency for sun.security.provider.* package

This is highlighted as "probably a bug" in my IDE.

E.g. `new byte[]{1}.equals(new byte[]{1})` is always false.
But `Arrays.equals(new byte[]{1}, new byte[]{1});` is true.

- The 4 replace methods were nearly identical.
- Deprecate String utility, which has a simple one-liner equivalent in the JDK
- Use DatatypeConverter for byte[] to hex. It's less code and even 2-3 times faster than the previous method.

OF-881: Simplify connection close semantics

- Use AtomicReference instead of synchronized block
- Extend java.io.Closeable; document contract
- Consolidate close/state transition logic

URLUTF8Encoder is obsolete due to `java.net.URLEncoder.encode(str, "UTF-8")`